The present invention relates generally to butterfly valves and more specifically to an improved valve seat for butterfly valves.
In early butterfly valves, the seat ring was bonded to a radially extending annular recess in the housing. This is illustrated specifically in FIG. 1. There is no adjustability of the amount of bulge or protrusion of the seat ring. The only pressures acting against it were those of the disc during engagement P.sub.D and axial forces only on the exposed edge from the fluid pressure P.sub.F. This provided uneven pressure distributions across the seat ring. When the valve seat had to be replaced or repaired, the valve is removed from the line, heated up until the bond between the seat ring and body is broken, the remaining epoxy chipped away and the new epoxy or vulcanizing is applied to a new seat ring in order to bond the seat into the body.
In U.S. Pat. No. 3,814,380 there is described an invention for an adjustable seat construction in a butterfly valve. That invention provides an adjustable seat construction which is inexpensive to manufacture, gives uniform pressure between a seat ring and disc, and thus can be operated with minimum torque, and allows replacement of the rubber seat ring in the field. The valve seat ring employs rectangular- or trapizoidal-shaped elastomer (e.g. rubber) seats which are either epoxy bonded or vulcanized into a machined recess in the valve body. A clamping ring with adjustable actuators provides adjustment for the seat ring. When the valve seat has to be replaced or repaired, the valve is normally removed from the line, heated up until the bond between the valve seat and body is broken down, the remaining epoxy is chipped away, and then new epoxy or vulcanizing is applied to a new seat in order to bond the seat into the body.
In pending U.S. patent application Ser. No. 154,545 entitled "Replaceable Adjustable Butterfly Valve Seat" to John P. Cunningham, there is described an invention for an adjustable seat construction for a butterfly valve wherein the seat ring is T-shaped and confined at one end by the transverse wall of an annular groove in the valve body and at the other end by a clamping ring which slides along the walls of the flow passage extending through the body. The clamping ring is forced against the seat ring by a plurality of individual screw actuators. The T-shaped elastomeric seat ring is held in place solely by the mechanical forces to facilitate removal, maintenance and replacement thereof. An example of this type of ring is illustrated in FIG. 2. The T-shaped ring seat 12 is received in the housing 10 and is held therein by a clamping ring 18 which adjustably compresses the seat ring 12 by an actuator which includes an annular ring 20 received in annular recess 22 of the housing and threaded actuators 24. Although the seat ring 12 is easily removed since it is not bonded to the housing, the compression and bulging of the seat ring are controlled by clamping ring 18 and the actuator assembly. The pressure from the fluid flow is no different than that of FIG. 1 for the bonded in the housing seat ring. The annular ring 20 absorbs the majority of the pressure created by the fluid P.sub.F and only the exposed axial surface 16 of the seat ring 12 is affected by the fluid pressure P.sub.F.
Another alternative to bonding the ring to the housing is illustrated in United Kingdom Patent Specification 1,000,912. An annular seat ring is bonded to an annular clamping ring set and secured to the housing by a plurality of threaded elements. The annular seat ring engages the housing along a radial plane and thereby lacks a locking action except for the threaded elements. As in the previous examples, the only exposed portion of the seat ring is that small portion which extends above the edge of the flow passage.
Accordingly, it would be desirable to have an adjustable butterfly valve seat that retains all of the advantages of the above-identified inventions, as well as includes a readily replaceable seat ring which is uniformly responsive to fluid pressure.